Cardiac responses during stimulation of the dorsal motor nucleus and nucleus ambiguus in the cat.

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Abstract
Studies were performed to determine the role of the dorsal motor nucleus (DMN) and nucleus ambiguus (NA) in caridac control in cats. Heart rate (HR), mean arterial blood pressure (MABP), ventricular contractility, left ventricular end-diastolic pressure (LVEDP) and right ventricular end-diastolic pressure (RVEDP) were monitored in anesthetized, paralyzed and .beta.-blocked animals. The rate of rise of the rising limb of the left ventricular pressure curve (dP/dt) and the output of a strain gauge sutured to the right ventricle (SGF) served as indices of ventricular contractility. Pacing electrodes were inserted into the ventricular myocardium and stimulating electrodes were stereotaxically palced in the DMN and NA. The nuclei were stimulated with and without cardiac pacing, before and after ipsilateral vagotomy. DMN stimulation produced decreases in MABP, dP/dt and SGF, no HR change and increases in LVEDP and RVEDP. HR and MABP decreased and dP/dt, SGF, LVEDP and RVEDP increased with NA stimulation. The responses to NA stimulation were abolished by ventricular pacing. The responses to stimulating either nucleus were abolished by ipsilateral vagotomy. The decreases in dP/dt and SGF with DMN activation were not secondary to preload decreases since LVEDP and RVEDP increased during stimulation. Since the dP/dt and SGF changes during NA stimulation were abolished by cardiac pacing, the responses were secondary to bradycardia. The data suggest cardiac vagal preganglionic somata are organized according to physiological function. Cell bodies of the DMN control ventricular contractility whereas NA somata are involved in HR control.